Efficient polarised output from end-pumped multirod resonators

Polarised radiation is required for many applications in optics. This paper describes several laser designs based on the variable configuration resonator, each capable of producing polarised output in a multirod resonator. Schematics for the designs are given and the modes of each cavity considered along with the stability of each resonator. Slope efficiencies as high as 45% and optical efficiencies of over 35% were observed in polarised operation with output powers as high as 10.2 W.     

Dielectric shielded nanoscale patch laser resonators

Dielectric shielded nanoscale patch laser resonators are introduced. Low-index dielectric shield layers surrounding a high-index core are shown to significantly reduce both metal and radiation losses. Structures suitable for both optical and electrical pumping and smaller than the vacuum wavelength in all three dimensions are shown to have a low enough threshold gain to lase at room temperature. Shifting the gain medium core provides control over the radiation pattern of the resonator and enables coupling of the laser light into a waveguide, opening opportunities for chipscale integration.     

Stabilization of the different frequency of reference and signal resonators in the Dulkyn gravitational-wave detector

It is shown that stabilization of the different frequency of optical radiations generated in the reference and signal resonators of the Dulkyn laser-interferometric gravitational-wave detector results in an efficient reevaluation of basic parameters describing the line widths of the laser radiation and the passive resonator, as well as the minimal laser power required to separate the valid signal from noises caused by natural fluctuations.     

Laser beam characteristic for laser resonators with diffraction optical elements

The matrix eigenvalue method is used to analyze a laser resonator composed of diffraction optical elements. The results show that this type of resonator can separate fundamental mode and high order modes effectively. The output beams can be designed for different requests.     

Coma compensation in off-axis laser resonators

Coma can introduce large linear losses in laser resonators with off-axis focusing. Compensation of coma and astigmatism is considered for a variety of resonator arrangements. It is demonstrated that it is only possible to compensate for both at a unique off-axis angle. A resonator design is proposed for eliminating coma and astigmatism.     

Simulation of optical field in laser resonators cavity by eigenvector method

In this paper, an Eigenvector method (EM) for the calculation of optical resonator modes and beam propagation is introduced, in which the transit matrix of an optical resonator is obtained by dividing the mirror into finite grids based on the Fresnel–Kirchoff diffractive integral equation. Then, the eigenvectors, representing the multimode characteristics of the resonator, can be calculated by solving the integral matrix eigenequation. The merits of EM include that the considerably simpler procedure of solution of eigenvectors of the matrix eigenequation replaces the complicated iteration in traditional methods, and there is no dependence on the initial field distribution, and a number of modes can be derived once and the discrimination capability of the resonator can be evaluated easily. The examples using EM to simulate con-focal resonators with small or large Fresnel numbers are given, and the calculated results, well matched with Fox–Li method or Lagueree–Gaussian approximation analytical solution, prove that EM is highly feasible and reasonable.     

Folded diffractive laser resonators with user-defined fundamental mode

The adjustment effort required for the alignment of laser resonators with arbitrarily shaped end mirrors can be significantly reduced by folding the resonator path half-way between the two end mirrors and by slightly tilting the resonator axis. Thus the resulting resonator consists only of one diffractive mirror and a plane mirror, and the separate alignment of both diffractive end mirrors with respect to each other can be avoided. This principle is demonstrated by a Nd:YAG laser with super-Gaussian output beam. Furthermore, it is shown theoretically that the influence of phase quantization effects on the beam quality can be strongly reduced as a consequence of the tilted resonator axis.     

Telescopic resonators for large-volume TEM00-mode operation

A stable resonator incorporating a suitably adjusted telescope gives reliable operation of an Nd:YAG laser with a large-volume TEM₀₀ mode. The telescope adjustment is chosen to minimize the effect of focal length variations in the laser rod and at the same time ensures the optimum mode-selection properties of a confocal resonator. Simple approximations applied to the ray transfer matrices allow a detailed analysis of the resonator to be performed. This analysis yields simple design equations relating the mode spot sizes, resonator length, telescope magnification and defocusing, and diffraction losses. Experimental results show excellent agreement with the results of this analysis.     

Investigations of active medium and of optical resonators of gasdynamic lasers

In the article is described the construction of a cw GDL based on combustion of CO, with the mixture exhausted to the atmosphere through a supersonic diffuser, as well as apparatus for the investigation of the physical properties of the active medium. The flow rate of the vibrational quanta converted into laser radiation at the input to the optical resonator is determined by calculation and experimentally. The main properties of the GDL active medium are investigated. The total losses in the optical resonator are determined and their influence on the output power is calculated. The operating conditions of the gasdynamic layer are experimentally optimized. A resonator with additional feedback is proposed.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 113, pp. 115–149, 1979.     

Generalized transfer function: A simple model applied to active single-mode microring resonators

The spectral properties of an active single-mode microring resonator are investigated in the frame of the generalized transfer function (GTF) approach, as derived from extended scattering and/or transfer matrix formalism. Spontaneous emission, looked upon as the driving source of the radiation, is described in a semi-classical way in the spectral domain. The internal and emitted fields are filtered into the resonance modes of the whole structure. The generalized transfer function expresses the spectral density of internal saturating intensity and includes all essential mechanisms at work in a laser oscillator: gain, losses and sources. The active zone is saturated through amplified spontaneous emission (ASE), integrated over its whole spectral range. Continuously valid across threshold, the method enables one to derive in a simple way the main steady-state properties of the laser oscillation, with the pumping rate as the only external parameter.     

Decay time of optical resonators

The decay time τ of an optical resonator depends on the special type of resonator (active, passive, homogeneous, inhomogeneous). Starting from a general expression for decay times, some special cases are derived and discussed in detail. It is shown, that the commonly used formulars give only lower or upper limits. These various relations are relevant for high gain laser with low reflectivities.     

Classical field theory methods in laser physics. III. Propagation of laser radiation in vacuum outside a resonator

The third Part of our work continues the analysis of the problem considered in Parts I and II [J. Russ. Laser Res.,17, 205 (1996);18, 2 (1997)]. We continue the search for the answer to the question: What is laser radiation from the viewpoint of the classical theory of wave fields? Here, we give one of the possible interpretations of propagation of laser radiation in vacuum outside a resonator from both the nonrelativistic and relativistic points of view. The relation between the metric and the radiation field structure is noted. Moreover, the third Part contains the conclusion concerning the work as a whole. It presents the main observations that may be useful for further studies of the problem.     

Effect of chromatic aberration on Gaussian beams: non-dispersive laser resonators

The propagation of a non-monochromatic (polychromatic) TEM₀₀ Gaussian beam in vacuum, its passage through a thin plate and its transformation by a thin lens are studied in the case of a non-dispersive laser resonator. The basic assumptions of the model are as follows: optical fields are stationary and plane-polarized, the paraxial wave equation is valid, an equivalent non-dispersive hemiconfocal resonator represents the lasing medium and its stable resonator, the laser emits in a single mode. It is also assumed that the plate and the lens have large transverse dimensions. Mathematical expressions, for beam radius, divergence, radius of curvature and beam parameter product, are obtained. A beam quality factor for polychromatic Gaussian beams is defined and its value calculated in each case of interest. It is proposed to simulate a dispersive laser resonator by a non-dispersive resonator complemented with a plate and/or a thin lens.     

Graded reflectivity mirror unstablelaser resonators

The graded reflectivity mirror (GRM) unstable resonator has become the resonator of choice for many solid-state laser systems. This tutorial review discusses through a step-by-step approach the inner workings of such resonators, in order to identify for potential designers and users tradeoffs which are involved in their design. Geometrical and diffractive contributions to the mode definition are discussed using a canonical formulation applicable to all types of unstable resonators. Particular attention is given to super-Gaussian resonators, which are nowadays the most widely used. The beam-shaping action of an amplifying medium is illustrated through a practical example, which makes clear the necessity to use a proper simulation software to predict correctly the behaviour of the resonator. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of a transverse magnetic field on the power and polarization of the radiation of a helium-neon laser at a wavelength of 3.39 μ

The dependence of the power and polarization of the radiation of a helium-neon laser on the value of a transverse magnetic field is studied. The effect of changes in the Q of the resonator under these conditions is also investigated. It is shown that it is possible for circularly polarized radiation to exist in a laser with Brewster windows.     

Influence of spherical aberrations on fundamental mode beam quality under different laser resonators

Spherical aberrations of the thermal lens of the active media are severe when solid state lasers are strongly pumped. The fundamental mode profile deteriorates due to the aberrations. Self-consistent modes of a resonator with aberrations are calculated by using the Fox--Li diffraction iterative algorithm. Calculation results show that the aberration induced fundamental mode beam quality deterioration depends greatly on the resonator design. The tolerance of a flat--flat resonator to the aberration coefficient is about 30λ in the middle of stability, where λ is the wavelength of laser beam. But for a dynamically stable resonator, 2λ of spherical aberration will create diffraction loss of more than 40%, if inappropriate design criteria are used. A birefringence compensated laser resonator with two Nd:YAG rods is experimentally studied. The experimental data are in quite good agreement with simulation results.     

Theoretical and experimental study on rare-eath element-doped silicon single-mode fiber laser with two different structures of resonators

Abstract: Laser resonator is very important in the study and fabrication of lasers. The work conditions and work parameters of rare-earth element-doped optical fiber lasers with two different structures of laser resonators, i. e., the fiber ring resonator and Fabry-Perot resonator are studied. The fineness, laser resonant conditions, laser oscillation conditions and threshold inversion of these two different cavity are deduced. A series of experiments are also given. The result is very valuable to evaluate the output of optical fiber laser and can be a foundation of device fabrication. The Nd~(3 )-doped silica single-mode fiber laser pumped by Ar~ laser with a low threshold of 1.02 mW and a maximum output of more than 1 mW are presented in this paper.     

Single-mode operation of diode lasers coupled to hemispherical resonators

Uncoated GaAs diode laser of different structures are coupled to external spherical mirrors. The emission characteristics of these systems are investigated. Mode selection effects are observed and single-mode operation may be achieved in the hemispherical resonator case if the length of the external cavity resonator is close to the optical diode length. Low coupling losses between the diode and the resonator are characteristic in this case and result in an increase of light output at coupling.     

Two-dimensional optical ring resonators based on radial Bragg resonance

A Bragg-reflection-based ring resonator is proposed and analyzed. Closed-form expressions for the field and dispersion curves for radial Bragg gratings and photonic bandgap crystals are derived. The required gratings exhibit a chirped period and a varying index profile. Small bending radii and strong control over the resonator dispersion are possible by the Bragg confinement. Large free spectral range and low radiation loss are predicted theoretically.